In recent years, lithium ion batteries have been used as chargeable secondary batteries in portable apparatuses such as digital cameras and portable phones. A lithium ion battery is generally susceptible to overcharging, overcurrent, and overdischarging, and is thus used in a battery pack having a protective circuit to protect the lithium ion battery by detecting overcharging, overcurrent, and overdischarging. Such a battery pack may be provided with a secondary battery monitoring circuit that detects the status of a lithium ion battery such as a remaining battery level.
There is a battery pack provided with a secondary battery monitoring circuit to which the voltage of a secondary battery is directly applied for detection of the voltage of the secondary battery (Patent Document 1, for example).